How to detect frauds in advertising business using machine learning?
There are a couple of different ways you can go about this depending on what kind of data you have.

If you have labels or can separate the normal data from the fraudulent, you can perform either binary classification, or likely more usefully, anomaly detection.

In Anomaly Detection(which is typically now done via autoencoder) you train your model on the normal data, so it learns a compressed representation of that 'signal', from there it will be able to detect any sample that does not fit the learned representation(in theory).

Here is a link to a tutorial in keras: link